Cutting Fondant Accents

Just a simple question about fondant. I've cut fondant inserts etc. with an xacto knife a few times, but have one problem. It seems when I start cutting, the fondant tends to stretch.Should I let the fondant dry slightly, or am I doing something wrong?For instance, If a want to cut a cross, I don't get sharp corners, or very straight lines I hope someone understands what I am trying to say, it's a little hard to explain. Thanks for any help.